Installing Go from source

Introduction

Go is an open source project, distributed under a
BSD-style license.
This document explains how to check out the sources,
build them on your own machine, and run them.

Most users don't need to do this, and will instead install
from precompiled binary packages as described in
Getting Started,
a much simpler process.
If you want to help develop what goes into those precompiled
packages, though, read on.

There are two official Go compiler tool chains.
This document focuses on the gc Go
compiler and tools (6g, 8g etc.).
For information on how to work on gccgo, a more traditional
compiler using the GCC back end, see
Setting up and using gccgo.

The Go compilers support three instruction sets.
There are important differences in the quality of the compilers for the different
architectures.

amd64 (a.k.a. x86-64); 6g,6l,6c,6a

A mature implementation. The compiler has an effective
optimizer (registerizer) and generates good code (although
gccgo can do noticeably better sometimes).

386 (a.k.a. x86 or x86-32); 8g,8l,8c,8a

Comparable to the amd64 port.

arm (a.k.a. ARM); 5g,5l,5c,5a

Supports Linux, FreeBSD and NetBSD binaries. Less widely used than the other ports.

Except for things like low-level operating system interface code, the run-time
support is the same in all ports and includes a mark-and-sweep garbage
collector, efficient array and string slicing, and support for efficient
goroutines, such as stacks that grow and shrink on demand.

The compilers can target the DragonFly BSD, FreeBSD, Linux, NetBSD, OpenBSD,
OS X (Darwin), Plan 9, Solaris and Windows operating systems.
The full set of supported combinations is listed in the discussion of
environment variables below.

Install C tools, if needed

The Go tool chain is written in C. To build it, you need a C compiler installed.
Please refer to the InstallFromSource
page on the Go community Wiki for operating system specific instructions.

Install Git, if needed

To perform the next step you must have Git installed. (Check that you
have a git command before proceeding.)

If you do not have a working Git installation,
follow the instructions on the
Git downloads page.

Fetch the repository

Go will install to a directory named go.
Change to the directory that will be its parent
and make sure the go directory does not exist.
Then clone the repository and check out the latest release tag:

(Optional) Switch to the master branch

If you intend to modify the go source code, and
contribute your changes
to the project, then move your repository
off the release branch, and onto the master (development) branch.
Otherwise, skip this step.

where the details on the last few lines reflect the operating system,
architecture, and root directory used during the install.

For more information about ways to control the build, see the discussion of
environment variables below.
all.bash (or all.bat) runs important tests for Go,
which can take more time than simply building Go. If you do not want to run
the test suite use make.bash (or make.bat)
instead.

Note: The go command will install the godoc
binary to $GOROOT/bin (or $GOBIN) and the
cover and vet binaries to
$GOROOT/pkg/tool/$GOOS_$GOARCH.
You can access the latter commands with
"gotoolcover" and
"gotoolvet".

Community resources

The usual community resources such as
#go-nuts on the Freenode IRC server
and the
Go Nuts
mailing list have active developers that can help you with problems
with your installation or your development work.
For those who wish to keep up to date,
there is another mailing list, golang-checkins,
that receives a message summarizing each checkin to the Go repository.

Keeping up with releases

New releases are announced on the
golang-announce
mailing list.
Each announcement mentions the latest release tag, for instance,
go1.4.

To update an existing tree to the latest release, you can run:

$ cd go/src
$ git fetch
$ git checkout <tag>
$ ./all.bash

Where <tag> is the version string of the release.

Optional environment variables

The Go compilation environment can be customized by environment variables.
None is required by the build, but you may wish to set some
to override the defaults.

$GOROOT

The root of the Go tree, often $HOME/go.
Its value is built into the tree when it is compiled, and
defaults to the parent of the directory where all.bash was run.
There is no need to set this unless you want to switch between multiple
local copies of the repository.

$GOROOT_FINAL

The value assumed by installed binaries and scripts when
$GOROOT is not set explicitly.
It defaults to the value of $GOROOT.
If you want to build the Go tree in one location
but move it elsewhere after the build, set
$GOROOT_FINAL to the eventual location.

$GOOS and $GOARCH

The name of the target operating system and compilation architecture.
These default to the values of $GOHOSTOS and
$GOHOSTARCH respectively (described below).

The name of the host operating system and compilation architecture.
These default to the local system's operating system and
architecture.

Valid choices are the same as for $GOOS and
$GOARCH, listed above.
The specified values must be compatible with the local system.
For example, you should not set $GOHOSTARCH to
arm on an x86 system.

$GOBIN

The location where Go binaries will be installed.
The default is $GOROOT/bin.
After installing, you will want to arrange to add this
directory to your $PATH, so you can use the tools.
If $GOBIN is set, the go command
installs all commands there.

$GO386 (for 386 only, default is auto-detected
if built on either 386 or amd64, 387 otherwise)

This controls the code generated by 8g to use either the 387 floating-point unit
(set to 387) or SSE2 instructions (set to sse2) for
floating point computations.

GO386=387: use x87 for floating point operations; should support all x86 chips (Pentium MMX or later).

GO386=sse2: use SSE2 for floating point operations; has better performance than 387, but only available on Pentium 4/Opteron/Athlon 64 or later.

$GOARM (for arm only; default is auto-detected if building
on the target processor, 6 if not)

This sets the ARM floating point co-processor architecture version the run-time
should target. If you are compiling on the target system, its value will be auto-detected.

GOARM=6: use VFPv1 only; default if cross compiling; usually ARM11 or better cores (VFPv2 or better is also supported)

GOARM=7: use VFPv3; usually Cortex-A cores

If in doubt, leave this variable unset, and adjust it if required
when you first run the Go executable.
The GoARM page
on the Go community wiki
contains further details regarding Go's ARM support.

Note that $GOARCH and $GOOS identify the
target environment, not the environment you are running on.
In effect, you are always cross-compiling.
By architecture, we mean the kind of binaries
that the target environment can run:
an x86-64 system running a 32-bit-only operating system
must set GOARCH to 386,
not amd64.

If you choose to override the defaults,
set these variables in your shell profile ($HOME/.bashrc,
$HOME/.profile, or equivalent). The settings might look
something like this:

export GOROOT=$HOME/go
export GOARCH=amd64
export GOOS=linux

although, to reiterate, none of these variables needs to be set to build,
install, and develop the Go tree.